In Patent Literature 1, there is a description of supplying a high-frequency low voltage to a compressor during shutdown at the time of heating. In Patent Literature 2, there is a description of supplying a single-phase AC voltage of 25 kHz, which is a higher frequency than that at the time of a normal operation, to a compressor, when the environment of an air conditioner has a low temperature.
The techniques described in Patent Literatures 1 and 2 are for heating the compressor or keeping the compressor warm to facilitate a lubricating effect inside the compressor by applying a high-frequency AC voltage to the compressor in accordance with drop of the ambient temperature.